C++ 环路终止条件

Question

I need to write a program which asks the user to input characters, until they input a vowel. However, my program always sets the condition to "true" and also does not stop the loop. Why is this happening?

#include <iostream>
using namespace std;
int main ()
{
    char ch;
    bool condition=false;
    char vow[5];
    vow[0]='a';
    vow[1]='e';
    vow[2]='i';
    vow[3]='o';
    vow[4]='u';

    char arr[1000];
    do
    {   
    condition=false;
    for (int i=0;i<1000;i++)
    {
         cout<<"Enter a character:\n";
         cin>>ch;
         arr[i]=ch;

         for (int k=0;k<5;k++)
         {
            if (ch==(vow[k]))
            {
                condition=true;
            }
        }
    }
    while (condition=false);
}

Answer 1

As many have already said in the comments, your the main thing you are doing wrong is that you put condition=false in your while head.

For some reason, the program works properly after making that change, though. Why is that?

What you are doing here is assigning false to your variable condition and afterwards compare it against != 0 which in boolean terms would mean != false .

So as a result you end up with something like this after compiling:
while((condition = false) != false) or while(false != false)
which evaluates to false and then breaks the loop. Together with your added change of using break as soon as you find a vowel, this makes your code 'work'.

Since it seems like you are new to programming here is your code with a few basic suggestions in the comments:

#include <iostream>

using namespace std;

int main ()
{
  char ch;
  bool condition = false;
  // You can initialize a primitive array in place without having to modify each value
  // individually.
  // Note however, you can not just reassign vow with this array initializer later on
  // but have to do it like you did before
  char vow[] = {'a', 'e', 'i', 'o', 'u'};
  char arr[1000];

  // To me it looks like you dont need the do...while loop around the for loop at all,
  // since you seem to want to break out of your loop the first time you find a vowel
  // anyways. Instead consider putting your condition as a seperate check into the
  // for header like this
  for (int i = 0; i < 1000 && !condition; i++) {
    cout << "Enter a character:\n";
    cin >> ch;
    arr[i] = ch;

    for (int k = 0; k < 5; k++) {
      if (ch == vow[k]) {
        condition = true;
      }
    }
  }

  // Dont forget the return statement. In your case its not really important since the
  // compiler adds return 0 by default, but for testing and such it can be very helpful
  return 0;
}

Also, using whitespaces and empty lines improves the readability of your code alot.
Of course, codestyle is always a bit of personal preference but I think everyone can agree to that:D

Answer 2

do
    {   
       for (int i=0;i<1000;i++)
        {
            cout<<"Enter a character:\n";
            cin>>ch;
            arr[i]=ch;

            for (int k=0;k<5;k++)
             {
                if (ch==(vow[k]))
                 {
                  x=1;
                 }
             }

            if (x==0)
            {  
                dis[i]=arr[i]; 
            }

            if(x==1)
            {
                break;
            }   

        count=i;    
        }


    }
    while (x=0);

making these changed fixed it. i don't know whether this is due to replacing while (condition=false) with while(x=0) or because of adding the if conditions. Any explanation on that would be appreciated:)